pushing themselves to the limit. But are they pushing too far? This may just be the most extreme fitness competition on Earth. A triumph of mind over muscle. Another man who is in the top five in the world in that regional event, James Hobart. Reporter: 28-year-old James Hobart is on a quest to be the fittest man on the planet. Don't get caught up looking left and right. You'd be better off keeping your head down and staying moving. Reporter: He's competing in 13 grueling events under the harsh sun of southern California. Crossfit has become a national sensation. Millions of Americans are obsessed with the high-intensity strength training program. And it's hard to argue with a body of evidence like this. Crossfit is also at the center of a fierce controversy. Accused of pushing people too hard too fast. No matter the consequences. The devotees insist these exercisers aren't to blame. The program is very safe. When applied properly with coaching and instruction. Reporter: Now, they're competing in the ultimate

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